This invention relates to protection of electrical equipment from transient surges in voltage, as from an external power source, especially by means of protective apparatus interposable between a conventional watt-hour meter and electrical loads downstream.
The desirability of protecting electrical meters and related equipment from voltage surges is well known. Similarly known are devices whose resistance varies non-linearly under applied voltage so that conduction therethrough is disproportionately greater at higher voltages than at normal lower voltages. A name for a class of such devices is "varistor".
Varistors connected to provide such surge protection have been installed within meters, as in Melanson U.S. Pat. No. 3,914,657 and in Zisa U.S. Pat. No. 3,725,745; and also in devices of plug-and-jack type adapted for use between electrical outlets and appliances to be operated by electricity drawn from such outlets, as in Orfano U.S. Pat. No. 4,089,032. Plug-and-jack devices for use between such an electric meter and the premises of an electricity customer include circuit-interrupting means (switches, with or without associated fuses), as suggested by Megarian in U.S. Pat. No. 3,599,047 and by St. John in U.S. Pat. No. 2,606,232. Interposition of a varistor or similar non-linear resistor between such a meter and downstream equipment at a customer's location is less apparent, notwithstanding that a need exists for a simple effective way to provide surge protection.